In the last few weeks of your pregnancy it's common to leak some urine when you cough, sneeze, laugh or lift something heavy.
It's caused by the sheer weight of the baby and the relaxing effect of progesterone.
For many women, the leaking will continue for some time after the birth - so keep on doing your pelvic floor exercises. For others, it may continue into later life.
'Bladder weakness affects one in three women over 40 who have had a pregnancy,' explains Dr Chris Steele, resident doctor on This Morning.
'If you weaken your pelvic floor through pregnancy or childbirth, you may leak urine when you laugh, sneeze, jump or have sex.'
Starting your pelvic floor exercises as early as possible will help. But the problem for most women is that, even if we remember to do them regularly, we are never quite sure if we're doing them right.
'Pull up and pull in,' advise Dr Chris, 'as if you're trying to stop yourself passing wind or stop the flow of urine when you're going to the loo. Hold for 10 seconds - you won't be able to manage that at first, but you'll improve.
'Do 10 of those, 10 times a day.'
For 90% of women, stress incontinence disappears after the birth, although it may take several weeks to settle down. In the meantime, use pantyliners or pads.
While bladder weakness is not uncommon in the early weeks after having a baby, you should seek advice from your GP if it doesn't improve.